How to lay triplex overhead service drop cable?
一、 What is Triplex overhead service drop cable?
The triplex aerial cable is mainly used to connect the incoming cable between the utility pole and the inlet, or the secondary distribution cable between the utility poles. Aerial insulated cables are overhead conductors equipped with insulation and protective sheaths, mainly single-core, and can be divided into hard aluminum wire structure, hard drawn copper wire structure, aluminum alloy wire structure, steel core or aluminum alloy according to their structure. Core support structure and self-supporting three-core twisted structure. It has the main characteristics of high power supply reliability, good power supply security, convenient erection and maintenance, and reasonable economy.
二、 What inspections need to be done before cable laying?
The single-core cables used in the three-phase system should be arranged in a close-fitting regular triangle (except for oil-filled cables and underwater cables), and should be fastened with straps every 1m.
(1) Whether the model and specifications meet the requirements, the insulation should be good, the appearance should be complete, and there should be no traces of trauma.
(2) In a three-phase four-wire system, a three-core cable plus a single-core cable (conductor) or cable metal sheath should not be used as a neutral line. Otherwise, when the triplex aluminum wire current is unbalanced, it is equivalent to the running state of a single-core cable, which is likely to cause power frequency interference. If it is an armored cable, the armor will heat up and even cause thermal breakdown of the insulation.
(3) The lengths of power cables running in parallel should be equal.
(4) A spare length should be reserved near the cable terminal head and the cable intermediate joint, and the direct buried cable should be laid in waves at the above two places to reserve a spare length.
(5) The distance of each fulcrum of the cable should be in accordance with the design regulations. When there is no design regulation, it should not be greater than: 1M horizontally for rubber and plastic cables, 2M vertically, and 0.75M horizontally for cables suspended on steel cables.
(6) The bending radius of the cable should not be less than 10 times the outer diameter of the cable (armoured or unarmored multi-core plastic insulated power cable).
(7) When the cable is laid, the cable should be led out from the upper end of the disc, and the friction and drag of the cable on the bracket and the ground should be avoided.
(8) Cables should not be crossed when laying, they should be arranged neatly, fixed, and sign boards should be installed.
(9) There should be firm stakes at the corners along the direct buried cables.
(10) When cables enter cable trenches, tunnels, buildings and pipes, the entrances and exits should be closed. Clamps and fixtures used for AC single-core cables shall not have a closed magnetic circuit composed of iron parts.
三、Main features of triplex overhead service drop cable
1. High power supply reliability: the overhead laying method greatly reduces the occurrence of various short-circuit faults.
2. High power supply safety: there is an insulating layer on the outside, which reduces the probability of electric shock casualties.
3. Convenient erection and maintenance: the overhead aluminum triplex wire cable can be erected on any kind of pole tower, or along the wall, and can also pass through the bushes under special circumstances, and be directly fixed on the tree pole with hardware. It can be erected in a single circuit, or multiple circuits can be erected on the same pole, without requiring a wide "electrical corridor". There is no need for special inspections for overhead cables, and there will be no short-circuit tripping accidents caused by flashover of branches, littering by residents, or accidental collision of crane arms, etc., thus greatly reducing the maintenance and repair work of the line.
4. Reasonable economy: Although the use of overhead cables is more expensive than the use of overhead bare wires, it is cheaper than ordinary underground cables. Therefore, although the one-time investment of overhead cables is slightly higher, the operating cost will be significantly lower than that of overhead bare conductors considering other factors. For example, the use of overhead cables makes the line gallery smaller, and even multiple lines share one tower, which reduces the cost of land acquisition and land occupation. There is no need to cut down and trim trees under the line during operation, which saves cutting and trimming costs. The most important thing is to reduce line failures and their direct or indirect damages incurred.